Apparatus and method for draining water from a cellulose web

ABSTRACT

An apparatus and a method are provided for draining water from a cellulose web which is formed in a wedge-shaped space defined by two wires, the wires being supported on chamber assemblies including at one time at least one water receiving chamber, the water flowing therein through the wire as a result of a pressure difference. Each water receiving chamber has connected thereto at least one substantially vertical pipe having a vertical drop between its top and bottom end sufficient for developing a gravitational suction leg in the water flowing pipe, and the pipe terminating in a water receiver.

This application is a 371 of PCT/FI01/00995 filed 16 Nov. 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for draining of water froma cellulose web, said web being formed in a wedge-shaped space definedby two wires, and said wires being supported by chamber assemblies,including at least one water receiving chamber at one time, the waterfrom suspension stock flowing therein through the wire as a result of apressure difference.

2. Description of Related Art

A web forming apparatus of the above type is prior known e.g. fromFinnish Patent Application No. 982539 to Metso Paper, Inc. In this priorknown apparatus, the water-receiving chambers set behind the wire areprovided with dewatering elements. It is an object of the presentinvention to provide an effective and simple alternative solution tothis dewatering system.

BRIEF SUMMARY OF THE INVENTION

An apparatus of the invention is characterized in that each receivingchamber is connected to at least one substantially vertical pipe, themounting thereof being such that vertical drops between the pipe's topand bottom end are sufficient for developing a gravitational tube leg inthe pipe in which the water is flowing.

A second characteristic feature of the invention is that the amount ofwater flowing from each water receiving chamber is measured and adjustedfor achieving a uniform formation of pulp web in a wedge-shaped spacedefined by wires.

A third characteristic feature is an orifice strip for delivering watertherethrough from a water receiving chamber into a vertical dischargepipe, as well as a compensating circulation for discharging a smallamount of water from a water receiving chamber from the side opposite tothe discharge pipe. Said perforated strip and said compensatingcirculation provide for a consistent draining of water from the webacross its entire width.

The inventive measuring of the amount of water discharging from a pulpweb can be implemented preferably in such a way that the waterdischarging vertical pipe terminates in a water receiver provided withat least one recess constituted by a sluice element, through which waterdischarges from the receiver in the form of a sluice flow, said flowbeing measured by means of a sluice flow meter. The measurement is asimple process, nor is it disturbed by possible impurities, such as airbubbles present in the liquid. It is obvious for a skilled person thatthe inventive measuring of discharging water can be implemented just aswell by other, prior known methods.

As for an apparatus of the invention, it is essential that the verticaldrop between the ends of a water discharging pipe be in such a magnitudethat the pipe develops a sufficient gravitational tube leg. The verticaldrop is preferably 4-10 m.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

The FIGURE shows a schematic of an apparatus according to one embodimentof the present invention implemented in a device for forming thecellulose web.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be described in more detail with reference to theaccompanying drawing.

Reference numeral 1 represents a web forming unit, comprising wireelements which establish a wedge-shaped space, the suspension stockbeing fed into said wedge-shaped space. On the opposite side of the wireare dewatering boxes, comprising several, for example six boxes, bothabove the top wire section and below the bottom wire section.

From dewatering boxes 2 present in the web forming unit 1, water ispassed through orifice strips 3 along pipes 4 and 5 for furtherprocessing. These pipes 4 and 5 comprise a comparatively lengthy,substantially vertical section, the purpose of said sections being tofunction as suction pipes, i.e. to establish a so-called suction leg. Asa result of a major vertical drop, a gravitational tube leg is developedby water in the flow pipes for replacing a traditional vacuum pumpsystem on the wire section of a drying machine. It should be noted thatthe flow rate must be sufficiently high, normally in excess of 2 m/s,for water-entrained impurities like air bubbles and gas bubbles andothers to be carried along with the flow instead of becoming depositede.g. in the upper elements of the apparatus.

A minor amount of water, normally about 10%, is discharged along pipes 6and 7 from the web forming unit 1 from the side opposite to the pipes 4and 5. This results in a consistent dewatering across the entire widthof a pulp web.

In the web forming unit 1, pressures are measured both on the side of apulp web and on the side of dewatering boxes. In the dewatering boxes,the pressure is measured both at the ends close to the discharge pipes 4and 5 and at those close to the discharge pipes 6 and 7.

The discharge pipes 4, 5, 6 and 7 are provided with valve elements forregulating a flow in the pipes.

The discharge pipes 4, 5, 6 and 7 terminate in a water receiver 8, whichfunctions as a water trap. This receiver 8 is provided with at least onerecess 9, which is positioned and dimensioned such as to establish asluice element for the water mass accumulated in the receiver 8. As thedimensions of the recess 9 and flow characteristics of water are known,the flow rate can be determined as based on the height of a liquid levelflowing in the recess. According to this height, it is now possible toadjust draining of water as desired from each dewatering box.

In the illustrated solution, the receiver 8 is circular incross-section, said receiver having its middle section provided with aseparate water tank for delivering the sluice flow therein.

The water draining from the receiver 8 in the form of a sluice flow isdelivered by means of a pump in a continuous flow along a pipe 10 forfurther processing.

In the present example, each dewatering chamber 2 is provided with thewater discharge pipe 4 and 5, as well as with the extra water dischargepipe 6 and 7 for a balanced dewatering process. It is obvious that thenumber of discharge pipes can always be varied as necessary withoutdeparting from the scope of the invention.

The inventive solution is simple, inexpensive, and effective regardingits implementation. The amount of water to be drained being adjustablespecifically in terms of each dewatering chamber and the uniformdrainage of water across the entire width of a pulp web improve the pulpweb in terms of its quality and uniformity. The suction effect createdby a vertical drop increases significantly the capacity of a pulp webformer and this augmented capacity is achieved without having to usesuction pumps which are expensive in terms of investment and operatingcosts. Measuring the amount of draining water by means of a sluicelevel, described as one conceivable implementation, constitutes aninexpensive, accurate, and reliable implementation.

1. An apparatus adapted to drain water from a cellulose web formed in awedge-shaped space defined by two wires supported by respective chamberassemblies, the chamber assemblies including at least onewater-receiving chamber, the wires being configured such that the waterfrom the web flows therethrough into the at least one water-receivingchamber, said apparatus comprising: a reservoir configured as a sluicefor collecting the water therein and adjustably draining the watertherefrom; and at least one discharge pipe operably engaged with the atleast one water-receiving chamber and adapted to channel the watertherefrom into the reservoir, the at least one discharge pipe having asubstantially vertical portion with a vertical drop extending between atop end and a bottom end thereof, the substantially vertical portionbeing configured to cooperate with the reservoir to provide agravitational suction leg for pulling the water from the at least onewater-receiving chamber.
 2. An apparatus according to claim 1 whereinthe vertical drop extends for between about 4 meters and about 10 metersfrom the top end to the bottom end.
 3. An apparatus according to claim 1further comprising a regulating element operably engaged with the atleast one discharge pipe between the at least one water-receivingchamber and the reservoir, the regulating element being adapted tomeasure and regulate an amount of the water channeled from the at leastone water-receiving chamber to the reservoir.
 4. An apparatus accordingto claim 1 wherein the reservoir further comprises a sluice flowmeasuring device operably engaged therewith for measuring an amount ofthe water drained from the reservoir.
 5. An apparatus adapted to drainwater from a cellulose web formed in a wedge-shaped space defined by twowires supported by respective chamber assemblies, the wires beingconfigured such that the water from the web flows therethrough into oneof the chamber assemblies, said apparatus comprising: at least onewater-receiving chamber operably engaged with the chamber assemblies andconfigured to receive the water flowing from the web through the wires;a reservoir configured as a sluice for collecting the water therein andadjustably draining the water therefrom; and at least one discharge pipeoperably engaged with the at least one water-receiving chamber andconfigured to channel the water therefrom into the reservoir, the atleast one discharge pipe having a substantially vertical portion with avertical drop extending between a top end and a bottom end thereof, thesubstantially vertical portion being configured to cooperate with thereservoir to provide a gravitational suction leg for pulling the waterfrom the at least one water-receiving chamber.
 6. An apparatus accordingto claim 5 wherein the vertical drop extends for between about 4 metersand about 10 meters from the top end to the bottom end.
 7. An apparatusaccording to claim 5 further comprising a regulating element operablyengaged with the at least one discharge pipe between the at least onewater-receiving chamber and the reservoir, the regulating element beingadapted to measure and regulate an amount of the water channeled fromthe at least one water-receiving chamber to the reservoir.
 8. Anapparatus according to claim 5 wherein the reservoir further comprises asluice flow measuring device operably engaged therewith for measuring anamount of the water drained from the reservoir.
 9. An apparatusaccording to claim 5 further comprising at least one extra dischargepipe operably engaged with the at least one water-receiving chamber, ingenerally opposing relation with respect to the at least one dischargepipe, for balancing the water drainage from the web.
 10. An apparatusaccording to claim 9 further comprising at least one orifice stripoperably engaged with the at least one water-receiving chamber andconfigured to direct the water therethrough to at least one of the atleast one discharge pipe and the at least one extra discharge pipe.